They used to say, of Broadway musicals deficient in melody but spectacular in design, that audiences came out “humming the sets.” Mirror Mirror, a tart twist on the Snow White fable, fumbles nearly every opportunity to be funny: the dialogue is flat, straining for wit it never achieves, and the pace is torpid when it should be bustling. But, the couture, darling, is hilariously divine. Julia Roberts, as the evil Queen of this fairy-tale realm, is first spotted in a gargantuan orange gown seated on a seashell throne that seems an extension of her dress; she looks as if she were in the process of being devoured by a ravenous mollusk. The courtiers’ clothes are a riot too: at a stately ball, handsome Prince Alcott (Armie Hammer) sports rabbit ears in his top hat and fuzzy bunny paws on his hands. So even if you’re as annoyed by the movie as I was, you’ll come out laughing the costumes.

All belated praise to Eiko Ishioka, the great designer whose apparel graced Broadway plays (M. Butterfly) and musicals (Spider-Man: Turn Off the Dark), circus spectacles (Cirque du Soleil’s Varekai) and the opening and closing nights of the Beijing Olympics. Ishioka, who died in January at 75, didn’t do many movies, but what she did was choice. Her costumes for Paul Schrader’s Mishima: A Life in Four Chapters and Francis Coppola’s Bram Stoker’s Dracula helped define the style of those lush, sepulchral films.

“The costumes are the sets,” Ishioka said in a documentary about her work with Coppola. Her attire certainly complements the riotous vistas envisioned by Tarsem Singh Dhandwar, the Indian-born director of Mirror Mirror, and before that of The Cell, The Fall and Immortals, for all of which Ishioka devised beguiling costumes. Whatever his lapses as a comedy director, Tarsem shared her connoisseur’s eye for cinematic luxe; and the clothes she confected for Mirror Mirror — another Roberts gown that suggests a veritable ostentation of peacocks, the saffron cloak with matching hoodie worn by Snow White (Lily Collins) — are as illuminating as Tom Foden’s grandiose production design, which have their own amusement value of a fairy-tale kingdom in a hashish dream. All right, you’ll come out laughing the sets, too.

But not the movie. A kind of medieval The Devil Wears Prada with aspirations of The Princess Bride‘s mix of romance and cunning comedy, Mirror Mirror also offers early hints that it will perform for the Snow White story what Wicked did for The Wizard of Oz: transform a presumed villainess into a misunderstood heroine. Doesn’t happen. The opening narration, spoken by Roberts, does carry a subversive tone, as when the Queen says the old kingdom was a happy place where the citizens sang and danced, adding acidulously, “Apparently nobody had a job back then; they just sang and danced.” Will Snow White prove to be a truculent child out of The Bad Seed or The Omen or Orphan, unjustly fouling the reputation of a devoted stepmom? She will not. She’s your standard plucky, stainless teen who, as in the Grimm fable, escapes the Queen’s death sentence, plays house with seven dwarfs and seals her destiny with Prince Charming with a perfect, reviving kiss.

And the movie’s Queen, instead of drumming up sympathy as a beautiful woman who must poignantly confront middle age in a land where only the very young get to be heroines, is the same old rotten parent. Roberts, who’ll turn 45 this fall, and whose performance is nothing if not game, submits herself to a beauty regimen that includes a mud pack of parrot poop and actual bee stings to give her lips that collagen plumpness. The Queen’s magic mirror image says she’s Her Majesty’s perfect reflection, except that “I have no wrinkles.” (“They’re not wrinkles,” the Queen protests. “They’re crinkles.”) Perfectly attuned to the young-female demographic that made The Hunger Games a mega-smash, Mirror Mirror requires of the moms who bring their daughters to the movie that they be able to laugh at lame jokes about their incipient decay. At least, that ageist prejudice isn’t unique to this film. From “Hansel and Gretel” to Tangled, the recent Disney take on “Rumpelstiltskin,” the Grimm canon is full of evil middle-aged women preying on young innocents.

The dwarfs fare better; this time they are highwaymen who learn to rob from the rich and give to the poor — they’re Merry Men with Snow White as their Robin Hood. The film manages to define each dwarf without naming them by their humors, as Disney did, and a few have distinguishing charm; especially good is Mark Povinelli as Half-Pint (the lovelorn one who looks like James Franco). They certainly are allowed more appeal than Hammer, who earned an Oscar nomination as the Winklevoss twins in The Social Network but here evinces only the befuddled, anodyne charm of the young Brendan Fraser. Nor can I add to the rapturous notices given Collins (daughter of Phil), who has been unaccountably heralded as the new Audrey Hepburn. Sacrilege! Hepburn was a screen beauty who radiated magical grace from every frame; Collins is poised but sullen, and sports the lavish eyebrows that a Hollywood makeup artist used to give leading ladies when they played frumps. We’ll take a teen Winona Ryder, or any brunette from the Disney Channel, over this No White.

Finally, Mirror Mirror is unfair to people expecting more than a few good laughs. Scenes proceed lethargically, with pauses after punch lines where Tarsem must hope for audience laughter. Anachronistic gags (as when the Prince tells Snow White that he has to be the hero because “it’s been focus-grouped — it works”) break whatever luscious spell the art direction and costumery might create. On their first meeting in the woods, the Prince tells the dwarfs, “You’re short, and it’s funny.” Well, the film is shortish (106 mins.) but it’s also epically unfunny. The producers should have handed the script to an actual clever person like Paul Rudnick (In & Out, Jeffrey) and told him to send it back in a week, with solid jokes and a buoyant spirit. Then audiences could leave Mirror Mirror not laughing the costumes but humming the movie.